Grease a 20 x 30 cm roasting pan and line the base with greaseproof paper.
Preheat the oven to 150C/300F/gas mark 2.
Melt the butter, soft brown sugar and treacle in a pan.
Sift the flour, ground ginger and cinnamon then stir in the melted mixture with the beaten eggs. Warm the milk to blood heat, pour it on to the bicarbonate of soda, stir it in and add it to the mixture. Stir well and pour the mixture into the prepared tin.
Bake the gingerbread for about 1 1/2 hours. Cover the top with greaseproof paper after 1 huor.
When the gingerbread is cold cut it into fingers and serve it spread with butter.